Researchers find many popular sites serving drive-by downloads

10 million people exposed to malware served by 25,000 most visited sites alone.

Researchers at Barracuda Labs have found that 58 among the 25,000 most popular websites were serving drive-by download exploits at some time in February.

The researchers used Alexa to determine the 25,000 most visited websites and scanned these sites during February. On 23 days, at least one of the sites was serving malware, and on the average day two sites were infected. In total, 58 different sites were found to be serving drive-by downloads in February.

At first glance, these numbers may not seem shocking. After all, just over 0.2% of the sites were infected and on an average day less than 0.01% of sites were serving malware. However, these sites attract many visitors: the researchers estimate that in February over 10 million users would have been exposed to malware through these sites. The number of people who visited one of many other compromised websites, or who were tricked into clicking a malicious link, may be many times higher.

They also point out that most of the infected sites have been running for a long time: over half of the sites were over five years old. Many users hold the generally incorrect belief that this means such a site is safe to visit.

A worrying example of how a popular website could serve malware to many users was seen last month, when popular Dutch news site nu.nl (which has an Alexa rank of 548) was serving malware to its visitors. It appeared that cybercriminals had gained access to the site's CMS in advance and started serving the malware around lunch time, when the site's visitor numbers usually peak. It only took an hour for the site to be cleaned, but by that time an estimated 100,000 people had been exposed to a variant of Sinowal.

More at the Barracuda Labs blog here, with further comments and an infographic at Threatposthere. Details of the nu.nl compromise can be found at Trend Microhere.

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